1. Field of Invention
The present invention relates to optical networking and more specifically, to a system and method for integrating CWDM and DWDM technologies on a common fiber optics infrastructure.
2. Description of Related Art
Coarse wavelength division multiplexing (CWDM) is a method of combining multiple signals on laser beams at various wavelengths for transmission along fiber optic cables. CWDM systems are a popular choice for metro access networks and major telecoms have a significant capital investment in the CWDM infrastructure. Although the number of channels in a CWDM system is fewer than in a dense wavelength division multiplexing (DWDM) system, CWDM remains widely deployed in metro access networks where the distance is limited to about 80 kilometers (km). As used herein, CWDM refers to an ITU (International Telecommunications Union) standard which includes the specification of the particular channel wavelengths and the spacing between these channels. DWDM refers to an ITU standard in which the channel spacing is tighter so more wavelength channels are packed into an optical fiber.
With the continued growth in network traffic, telecoms are motivated to upgrade the capacity of their network to meet customer expectations. This means that telecoms need to increase channel density by adding additional wavelengths. However, CWDM is effectively limited to about eight different wavelengths on common ITU-T G.652 fiber (type A and B). The G.652a and G.652b specifications define the optical fiber specifications. These optical fibers are typically found in extended length LAN, MAN and access network systems. Clearly, rather than ripping out the CWDM network and replacing it with a DWDM network, telecoms need a cost effective solution that can increase channel density by adding wavelengths in a seamless, non-evasive manner to the CWDM network.
On approach that has been suggested is to cannibalize a portion of the CWDM wavelengths to route DWDM channels. Because, DWDM has tighter channel spacing, replacing 25% to 50% of the CWDM channels with DWDM channels results in an overall increase in channel density. Unfortunately, this approach has several shortcomings. For example, the telecom loses a significant portion of their CWDM bandwidth, which is clearly undesirable. Further, because of the optical characteristics of the 1 GbE and 10 GbE, performance is degraded and the network is limited to much less than 80 kilometers (km). Thus, the telecom would have to redesign the entire network to take into account the degraded performance. Further still, the DWDM channels undergo significantly more attenuation than the CWDM channels which is a critical limitation for 10 G application already suffering a power budget gap with ½ GbE CWDM channels.
Notwithstanding the problems with adding addition channels, telecoms are also motivated to upgrade the data rates of their network to meet customer expectations. This means that telecoms need to increase data rates on at least part of the channel capacity. Since most of the installed CWDM networks already include the technology infrastructure to support 1 Gigabit Ethernet (GbE), the natural progression would be to upgrade the CWDM infrastructure to handle 10 GbE. However, because DWDM technology dominates the 10 GbE market, there is only limited market opportunity for 10 GbE CWDM technology and the acquisition price for that technology too high. Thus, telecoms are being forced to upgrade their infrastructure to 10 GbE DWDM.
The upgrade to 10 GbE DWDM means that telecoms either have to string new fiber or mix DWDM with CWDM optical technologies on the same fiber. Unfortunately, because the 10 G optics has a reduced power budget compared to the lower speed GbE optics, it is not possible to simply insert 10 G optics on existing CWDM installations because any optical amplification of the DWDM would block the CWDM wavelengths that are outside the pass band of the amplifiers.
Accordingly, most telecoms resort to leaving the traditional CWDM network intact and stringing a separate fiber to handle the DWDM network traffic. Not only is this an expensive alternative, laying new fiber is intrusive and potentially disruptive to the existing network as new power supplies and other infrastructure is swapped out to handle the new network.
What is needed is a system and method that increases the channel density of CWDM networks and migrates the CWDM networks to 10 GbE in a seamless and non-invasive manner.